A device is known in which a damping force produced by the hydraulic damping device is regulated on the basis of an external operation. An operation rod is axially disposed through a piston rod of the hydraulic damping device. A valve is provided on the tip of the rod in order to vary the damping force. The opening of the valve is varied in response to minute regulation of the axial position of the operation rod. Thus it is possible to regulate the damping force generated by the hydraulic damping device.
However since the operation rod is disposed coaxial with respect to the piston rod, the structure of the device becomes complicated. Furthermore this operation is adversely affected since the position of the operation rod results in a position which tends to interfere with the vehicle body. In addition, the basic length of the hydraulic damping device in an axial direction is increased. The function regulating the damping force is simple due to the fact that only the opening of the valve is varied. As a result, the generated damping force at a high piston speed region in the hydraulic damping device can not be regulated separately from the generated damping force at in a low piston speed region.